Universal multifractal Martian topography
Summary: In the present study, we investigate the scaling properties of the topography of Mars. Planetary topographic fields are well known to exhibit (mono)fractal behavior. Indeed, fractal formalism is efficient in reproducing the variability observed in topography. Our results suggest a multifractal behavior from the planetary scale down to 10 km. From 10 km to 300 m, the topography seems to be simple monofractal.
Nonlin. Processes Geophys., 22, 713-722, doi:10.5194/npg-22-713-2015, 2015
A dynamical systems approach to the surface search for debris associated with the disappearance of flight MH370
Summary: The disappearance of Malaysia Airlines flight MH370 on 8 March 2014 is one of the great mysteries of our time. The most relevant aspect is that not a piece of debris was found during the intensive surface search carried out for roughly 2 months following the crash. By combining different ocean data with dynamical systems tools, we propose a revised search strategy by showing why debris could not have been expected in some targeted search areas and determining regions where debris could be.
Nonlin. Processes Geophys., 22, 701-712, doi:10.5194/npg-22-701-2015, 2015
Efficient Bayesian inference for natural time series using ARFIMA processes
Nonlin. Processes Geophys., 22, 679-700, doi:10.5194/npg-22-679-2015, 2015
Local finite-time Lyapunov exponent, local sampling and probabilistic source and destination regions
Summary: In this paper a new interpretation of the local finite-time Lyapunov exponent is proposed. This concept can practically assist in field experiments where samples are collected at a fixed location and it is necessary to attribute long-distance transport phenomena and location of source points to the characteristic variation of the sampled particles. Also, results of this study have the potential to aid in planning of optimal local sampling of passive particles.
Nonlin. Processes Geophys., 22, 663-677, doi:10.5194/npg-22-663-2015, 2015
Expanding the validity of the ensemble Kalman filter without the intrinsic need for inflation
Summary: The popular data assimilation technique known as the ensemble Kalman filter (EnKF) suffers from sampling errors due to the limited size of the ensemble. This deficiency is usually cured by inflating the sampled error covariances and by using localization. This paper further develops and discusses the finite-size EnKF, or EnKF-N, a variant of the EnKF that does not require inflation. It expands the use of the EnKF-N to a wider range of dynamical regimes.
Nonlin. Processes Geophys., 22, 645-662, doi:10.5194/npg-22-645-2015, 2015
Intermittent particle dynamics in marine coastal waters
Summary: Intermittent dynamics of particle size distribution in coastal waters is studied. Particle sizes are separated into four size classes: silt, fine, coarse and macro particles. The time series of each size class is derived, and their multiscaling properties studied. Similar analysis has been done for suspended particulate matter and total volume concentration. All quantities display a nonlinear moment function and a negative Hurst scaling exponent.
Nonlin. Processes Geophys., 22, 633-643, doi:10.5194/npg-22-633-2015, 2015
Earthquake source parameters that display the first digit phenomenon
Nonlin. Processes Geophys., 22, 625-632, doi:10.5194/npg-22-625-2015, 2015
Using sparse regularization for multi-resolution tomography of the ionosphere
Nonlin. Processes Geophys., 22, 613-624, doi:10.5194/npg-22-613-2015, 2015
A framework for variational data assimilation with superparameterization
Summary: Superparameterization is a multiscale computational method that significantly improves the representation of cloud processes in global atmosphere and climate models. We present a framework for assimilating observational data into superparameterized models to initialize them for forecasts. The framework is demonstrated in the context of a new system of ordinary differential equations that constitutes perhaps the simplest model of superparameterization.
Nonlin. Processes Geophys., 22, 601-611, doi:10.5194/npg-22-601-2015, 2015
Brief Communication: Earthquake sequencing: analysis of time series constructed from the Markov chain model
Summary: We introduced a new modified Markov chain model to generate a time series of the earthquake sequences from a global catalogue with an optimum time sampling of 9 days. Here, we subject the time series to a known analysis method namely an ensemble empirical mode decomposition to study the state-to-state fluctuations in each of the intrinsic mode functions. Also, we establish the power-law behaviour of the time series with the Fano factor and Allan factor used in time-correlative behaviour studies
Nonlin. Processes Geophys., 22, 589-599, doi:10.5194/npg-22-589-2015, 2015
Identification of magnetic anomalies based on ground magnetic data analysis using multifractal modelling: a case study in Qoja-Kandi, East Azerbaijan Province, Iran
Nonlin. Processes Geophys., 22, 579-587, doi:10.5194/npg-22-579-2015, 2015
A method to calculate finite-time Lyapunov exponents for inertial particles in incompressible flows
Summary: The present study aims to improve the calculus of finite-time Lyapunov exponents (FTLEs) applied to describe the transport of inertial particles in a fluid flow. To this aim, the deformation tensor is modified to take into account that the stretching rate between particles separated by a certain distance is influenced by the initial velocity of the particles. Results are presented for two different flows and compared with the classical method by Shadden (2005).
Nonlin. Processes Geophys., 22, 571-577, doi:10.5194/npg-22-571-2015, 2015
Review: visual analytics of climate networks
Summary: The paper reviews the available visualisation techniques and tools for the visual analysis of geo-physical climate networks. The results from a questionnaire with experts from non-linear physics are presented, and the paper surveys recent developments from information visualisation and cartography with respect to their applicability for visual climate network analytics. Several case studies based on own solutions illustrate the potentials of state-of-the-art network visualisation technology.
Nonlin. Processes Geophys., 22, 545-570, doi:10.5194/npg-22-545-2015, 2015
The transient variation in the complexes of the low-latitude ionosphere within the equatorial ionization anomaly region of Nigeria
Summary: This paper describes chaos and dynamical complexity to reveal the state of the underlying dynamics of the ionosphere on a daily basis. This is to show the daily/transient variations of chaoticity and dynamical complexity so as to reveal the degree of changes that occur in the ionospheric process and dynamics from one day to another. This paper will point the space science community in the direction of the use of chaoticity and dynamical complexity as indices to describe the process and dynamics.
Nonlin. Processes Geophys., 22, 527-543, doi:10.5194/npg-22-527-2015, 2015
Systematic attribution of observed Southern Hemisphere circulation trends to external forcing and internal variability
Nonlin. Processes Geophys., 22, 513-525, doi:10.5194/npg-22-513-2015, 2015
Earthquake sequencing: chimera states with Kuramoto model dynamics on directed graphs
Summary: Earthquake sequencing is an intriguing research topic and the dynamics involved are complex. For directed graphs that represent earthquake sequencing, the Kuramoto model yields synchronization. Inclusion of non-local effects evokes the occurrence of chimera states or the co-existence of synchronous and asynchronous behavior among earthquake zones. It is the chaotic dynamics of them resulting in certain patterns that we begin to see in the sequence of seismic events with a very simple model.
Nonlin. Processes Geophys., 22, 499-512, doi:10.5194/npg-22-499-2015, 2015
Spectral diagonal ensemble Kalman filters
Summary: A new type of ensemble Kalman filter for data assimilation is developed, based on fast Fourier transform and wavelet transform. The method can work with minimal computational resources. We develop variants for several general types of observations, give a rigorous proof that the method improves the approximation of the state covariance, and present computational experiments showing that the new technique works reliably with very small ensembles and is stable over multiple analysis cycles.
Nonlin. Processes Geophys., 22, 485-497, doi:10.5194/npg-22-485-2015, 2015
Search for the 531-day-period wobble signal in the polar motion based on EEMD
Summary: A 531-day wobble (531 dW) signal is clearly detected with a mean amplitude of about 7 mas after applying the ensemble empirical mode decomposition (EEMD) to the 1962-2013 polar motion (PM) time series. This signal is also detected in the two longest available superconducting gravimeter (SG) records. Synthetic tests are carried out to explain why the 531 dW signal can only be observed in recent 30-year PM time series after using EEMD.
Nonlin. Processes Geophys., 22, 473-484, doi:10.5194/npg-22-473-2015, 2015
Direct numerical simulation of intermittent turbulence under stably stratified conditions
Summary: The present work, to the best of our knowledge, is the first DNS study reporting temporal (long-term) statistics of intermittent turbulence (a.k.a. bursting events) in stably stratified flows. The present paper not only accurately reproduces recently published key spatial statistics of intermittent turbulence but also reports some intriguing features, e.g., the coexistence of internal waves and intermittent turbulence.
Nonlin. Processes Geophys., 22, 447-471, doi:10.5194/npg-22-447-2015, 2015
Global terrestrial water storage connectivity revealed using complex climate network analyses
Summary: Terrestrial water storage (TWS) plays a key role in global water and energy cycles. This work applies complex climate networks to analyzing spatial patterns in TWS. A comparative analysis is conducted using a remotely sensed (GRACE) and a model-generated TWS data set. Our results reveal hotspots of TWS anomalies around the global land surfaces. Prospects are offered on using network connectivity as constraints to further improve current global land surface models.
Nonlin. Processes Geophys., 22, 433-446, doi:10.5194/npg-22-433-2015, 2015